Solvents such as propane, butane, propene, butene and mixtures thereof are usually recovered for reuse by processes whereby the solvent is permitted to vaporize to thereby become separated from the dewaxed oil and this recovered vapor is then subjected to high energy compression to be reliquified for reuse. It is subsequently cooled to the low temperature required for dewaxing. While this results in the recovery of substantially pure solvent, it is extremely energy intensive and not very economical.
Less energy intensive systems have been investigated for the recovery of these light hydrocarbon autorefrigerative dewaxing solvents.
In U.S. Pat. No. 4,595,507 it is taught that mixtures of heavy oils and light hydrocarbons may be separated by passing the mixture through a polymeric membrane. The membrane used comprises a polymer which is capable of maintaining its integrity in the presence of hydrocarbon compounds and which has been modified by being subjected to the action of a sulfonating agent. Sulfonating agents include fuming sulfuric acid, chlorosulfonic acid, sulfur trioxide, etc. The surface or bulk modified polymer will contain a degree of sulfonation ranging from about 15 to about 50%. The separation process is effected at temperatures ranging from about ambient to about 100.degree. C. and pressures ranging from about 50 to 1000 psig. The process is described as useful for separating heavy oils from relatively light hydrocarbons which have been used as solvents in the various hydrocarbon treatment processes. The light hydrocarbon is recovered as the permeate. The membrane used may possess a wide range of pore sizes ranging from about 10 to about 500 Angstroms. The membranes are made from polymers which have solubility factors sufficiently different from those of the light hydrocarbon solvents in order to avoid dissolution of the membrane in the solvent. The membranes are made from polymers having solubility parameters in excess of about 9.0. Membranes which can be useful include those made from polysulfone, polycarbonate, cellulose acetate, poly-acrylonitrile, polyvinylalcohol, Nylon 6,6, Nylon 8, cellulose, polybenzemidazole, polyamide, polyimide, polytetrafluoroethylene.
U.S. Pat. No. 4,617,126 teaches that mixtures of heavy oil and light hydrocarbons may be separated by passing the mixture over a polymeric membrane which comprises a polymer capable of maintaining its integrity in the presence of hydrocarbon compounds at temperatures ranging from about ambient to about 100.degree. C. and pressures ranging from about 50 to 1000 psi. The membranes possess pore sizes ranging from about 10 to about 500 Angstroms and are cast from a solution.
The membrane is made from polymeric material which, having a different solubility parameter than the light hydrocarbon, does not dissolve in the light hydrocarbon. The polymers possess solubility parameters in excess of 9.0 and include polysulfone, polycarbonate, cellulose acetate, polyacrylonitrile, polyvinyl alcohol, Nylon 6,6, Nylon 8, cellulose, polybenzoimidazole, polyamide, polyimide, polytetrafluoroethylene.
The solvents recovered can include ethanol, propanol, butanol, propane, n-pentane, iso-pentane, n-hexane, n-heptane. The membranes are prepared by dissolving the polymer in a casting solvent to produce a casting solution. The casting solvents include N-methyl 2-pyrollidone, dimethylformamide, dimethylsulfoxide, dichloromethane, dichloroethane, chloroform, methyl cellusolve, propylene glycol or mixtures thereof such as DMF/methyl cellusolve, NMP/propylene glycol, NMP/DMSO etc.